Improved phase stability of γ-CsPbI3 perovskite nanocrystals using the interface effect using iodine modified graphene oxide

Inorganic perovskites featuring cesium lead tri-iodide (CsPbI3) have shown great potential in optoelectronic applications. However, CsPbI3 still suffers from poor crystal phase stability. Here, we compare the difference in the stability of gamma-phase (γ-) CsPbI3 NC growth on thermally-reduced graphene oxide (rGO) and iodine-modified rGO, and discuss the mechanism of the interface effect of active elements on the surface of rGO on the stability of γ-CsPbI3 NCs. The results show that thermally-reduced rGO presents only the O-site on the surface of graphene, which leads to irregular shapes, low coverage, poor size distributions, and further a compressive stress of γ-CsPbI3 NCs on it, which possesses an adverse effect on the phase stability. In contrast, iodine-modified rGO is beneficial for maintaining the phase stability and morphology of γ-CsPbI3 NCs, and increasing their amounts on the surface of rGO, and further improving their optoelectronic properties due to the iodine modulation. More importantly, the active element on the surface of rGO changing from the O- to I-site leads to the stress state of γ-CsPbI3 NCs converting into a tensile stress, which plays an important role in stabilizing the black perovskite phase of the NCs. Furthermore, we optimize the active iodine amount and concentration of the iodine-modified rGO to examine the interface effect and how it stabilizes the black perovskite phase of γ-CsPbI3 NCs. The optimized γ-CsPbI3 NCs/rGO heterostructured thin films showed a photoluminescence quantum yield (PLQY) of 10.5% and retained approximately 80% of its initial PLQY after aging in air (25 °C and 25% relative humidity) under dark conditions for a month.